This invention relates to a polyethylene terephthalate composition improved in molding workability, which can give stable physical properties of a molded product even when a slight amount of water exists at the time of molding working and the composition dwells in a molding machine for a long time.
Polyethylene terephthalate has been used widely in various industrial fields as engineering plastic having excellent mechanical and physical properties. However, since polyethylene terephthalate is a polyester having a high melting point, it has a drawback that hydrolysis occurs within an extremely short time at the time of molding working due to a small amount of water contained in pellets, whereby mechanical and physical properties of a molded product are lowered significantly and also "molding flash"0 is formed on a parting line of a product.
In order to solve such a drawback of polyethylene terephthalate, many techniques to cope with the drawback have been reported, but the drawback has not yet solved completely.
Thus, when polyethylene terephthalate is molded, it is still required that before molding, a pellet should be dried sufficiently, supplied in a molding machine while keeping its water content 100 to 200 ppm, and heated and melted within a short time to complete an operation. Under the present conditions, although polyethylene terephthalate has excellent mechanical, physical and thermal properties inherently when compared with polybutylene terephthalate, development of its market has been delayed because of such cumbersome water control of pellets and control of molding conditions.
Previously, the present inventors accomplished an invention to solve these problems of a polyethylene terephthalate composition (Japanese Provisional Patent Publication No. 302462/1990), and further investigated to solve the above-mentioned problems by using another composition.